This invention relates to an improved process for the production of N,O-disubstituted urethanes by reacting substituted ureas with alcohols. The products obtained by this process are particularly useful in the production of the isocyanates on which they are based.
It is known that urethanes may be formed by reacting organic isocyanates with alcohols. This reaction is reversible, i.e., urethanes may be thermally split into the isocyanate and the alcohol on which they are based (see, for example, U.S. Pat. No. 2,409,712). Urethanes which may be thermally split into isocyanates are, therefore, potential starting materials for the production of such isocyanates.
Isocyanates are commercially produced to a very large extent by reacting primary amines with phosgene. The production of urethanes without phosgene and the subsequent thermal splitting thereof would be an interesting alternative to this commercially used method. One method of producing urethanes without the use of phosgene which has been explored is a reaction of substituted ureas with alcohols in a manner such as that described in U.S. Pat. Nos. 2,409,712. However, this known method produces insufficient amounts of the urethane for commercial purposes. The inadequate yields obtained from the procedure of U.S. Pat. No. 2,409,712 are attributable to the fact that the primary amine corresponding to the urea substituent forms as a secondary product.